An image forming apparatus, such as a copying machine, a printer or a multifunction peripheral, is sometimes constructed such that an image carrier on which an electrostatic latent image is formed, such as a photosensitive drum, a charging device, a cleaning device or the like are integrated into a unit and this unit is attachably/detachably supported to an apparatus main body by sliding operation. In an image forming apparatus for full color, since the units for every color are provided, in order to prevent color displacement, each of the units needs to be positioned with respect to the apparatus main body with a high precision.
In order to position each of the units with respect to the apparatus main body, there may be a case in which a retainer made of a metal plate is used. The retainer is a positioning member having a bearing hole into which a front end of a rotating shaft of the image carrier of each unit is to be inserted. In such each unit, a rear end of the rotating shaft of the image carrier is inserted into a shaft supporting hole formed in the apparatus main body and the front end of the rotating shaft is held in the bearing hole of the retainer. Then, by positioning the retainer with respect to the apparatus main body, it makes possible to improve a precision of a relative position of each image carrier.
As a construction to position each unit by employing the retainer, in Patent Literature 1, there is proposed an image forming apparatus configured such that a front end of a rotating shaft of an image carrier is held in a shaft supporting hole formed in the retainer by self-weight. This image forming apparatus is further provided with a pressing member to press and position the rotating shaft held in the shaft supporting hole and a sliding member to slide the pressing member between a pressing position where the pressing member presses the rotating shaft and a non-pressing position where the pressing member comes into non-contact with the rotating shaft.